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Change in ATP-pyrophosphohydrolase activity during spherule formation of Physarum polycephalum
Abstract:
The activity of Ca2+-dependent ATP pyrophosphohydrolase was found to fluctuate during spherule formation of the acellular slime mold Physarum polycephalum under starving incubation. The enzyme activity increased up to 16-fold at the 3rd day of the starvation, then decreased drastically to less than its original level. Column chromatography of the enzyme preparation suggested that the increase in the activity was due to de novo synthesis of a new isozyme. Cycloheximide inhibited the synthesis. The two isozymes were different in their Ca2+ sensitivity, the new one being less sensitive.
Insights
During starvation-induced spherule formation, Physarum polycephalum showed fluctuating Ca2+-dependent ATP pyrophosphohydrolase activity. A new, less calcium-sensitive isozyme was synthesized, increasing activity significantly before declining.
Area of Science:
- Biochemistry
- Cell Biology
- Mycology
Background:
- The acellular slime mold *Physarum polycephalum* undergoes significant morphological and biochemical changes during starvation-induced spherule formation.
- Calcium-dependent ATP pyrophosphohydrolase plays a role in cellular energy metabolism, but its dynamic regulation during developmental processes is not fully understood.
Purpose of the Study:
- To investigate the activity patterns of Ca2+-dependent ATP pyrophosphohydrolase during spherule formation in *Physarum polycephalum* under starvation conditions.
- To identify the molecular basis for observed changes in enzyme activity, specifically exploring the potential synthesis of new isozymes.
Main Methods:
- Culturing *Physarum polycephalum* under starvation conditions to induce spherule formation.
- Measuring Ca2+-dependent ATP pyrophosphohydrolase activity at different time points during starvation.
- Utilizing column chromatography to analyze enzyme preparations and identify different isozymes.
- Employing cycloheximide to assess the role of protein synthesis in enzyme activity changes.
Main Results:
- Ca2+-dependent ATP pyrophosphohydrolase activity exhibited a marked fluctuation, increasing up to 16-fold by the third day of starvation before decreasing below the initial level.
- Column chromatography indicated that the surge in activity was attributable to the de novo synthesis of a novel isozyme.
- Cycloheximide treatment effectively inhibited this synthesis, confirming the role of active protein synthesis.
- The newly synthesized isozyme demonstrated reduced sensitivity to calcium compared to the original form.
Conclusions:
- The synthesis of a new, less calcium-sensitive isozyme of Ca2+-dependent ATP pyrophosphohydrolase is a key event during starvation-induced spherule formation in *Physarum polycephalum*.
- This dynamic regulation of enzyme activity and isozyme composition likely plays a crucial role in the developmental transition and survival strategies of the organism under nutrient deprivation.